The New Zealand Qualifications Authority is refusing to say why its computer system crumbled under pressure when thousands of students attempted to access their NCEA results yesterday.

The government department is staying tight-lipped on why its system wasn't able to cope when thousands of students logged on to view their results, or whether it would specifically address the issue ahead of next year's release.

Students had been waiting all summer to learn of their marks, and were frustrated when they had to continue to wait because the system couldn't cope with the demand.

Instead of their results, they were confronted with a message saying the site was experiencing heavy usage.

Some said they had been trying to log on for 12 hours before they were given access while others had to wait until this morning.

Liz Feinson said yesterday was frustrating for both her and her daughter Alex, who tried all day to log on.

"Sometimes she gets to the login phase and then is bumped out of the site and then it tells her that she's used up her login allocation and to try later. I have tried to login all day on her behalf as well and the same has happened to me," Feinson said.

"What a joke. The website must be managed by the same people who manage the teachers' payroll."

Alex, 16, gave up last night but was able to access her results this morning. Another mother said she repeatedly tried to log on from just before 9am until 9pm, when she finally had access.

Close to 70,000 students had viewed their results by 9pm last night, NZQA deputy chief executive Richard Thornton said.

"NZQA tested services extensively before results were released. Throughout the day NZQA actively managed the system to improve its performance under high demand," Thornton said in a statement.

"To ensure students could receive assistance with passwords and NSN numbers NZQA also extended the hours of its call centre which yesterday operated throughout the night."

Thornton would not respond to specific questions about why the system did not cope under the pressure, whether it had failed to cope in the past, or if NZQA specifically intended to review its computer system.

"As part of our annual review of the NCEA examination cycle NZQA considers changes or improvements to our systems and processes for the benefit of learners," Thornton said.